1. Field of the Invention
The present invention relates to a normally closed electromagnetic valve and more particularly to improvements in a normally closed electromagnetic valve comprising a cylindrical valve housing having a thin wall, a valve seat member fitted in and fixed to one end of the valve housing, a fixed core fixed liquid-tightly to the other end of the valve housing, a movable core forming a valve chamber with the valve seat member and housed in the valve housing opposed to the fixed core, a valve body fixed to the movable core seatably on a valve seat formed on the valve seat member facing the valve chamber, a return spring provided between the fixed core and the movable core giving a spring force that causes the valve body to be seated on the valve seat and a coil for generating an electromagnetic force that causes the movable core to be attracted to the fixed core during excitation, the valve housing being housed in a mounting hole provided open on one side of a substrate on one end thereof in such an arrangement that the valve housing is restricted in axial movement toward the interior of the mounting hole.
2. Description of the Related Art
Such a normally closed electromagnetic valve has heretofore been known, e.g., in JP-A-7-151258. In accordance with this disclosure, in order to mount a normally closed electromagnetic valve on a substrate with a valve housing housed in a mounting hole on one end thereof, a coil case covering a coil is provided in contact engagement with a stepped portion provided facing axially outwardly and a retainer ring provided in contact engagement with the coil case on the axially external side thereof is pressed in the external end of the mounting hole.
However, since the aforementioned related art normally closed electromagnetic valve has such an arrangement that the normally closed electromagnetic valve is incorporated in the substrate by pressing the retainer ring in the external end of the mounting hole, it can hardly be said that this type of a normally closed electromagnetic valve has a good mountability. This type of a normally closed electromagnetic valve finds difficulty in recycling because the valve housing can be difficultly detached from the substrate.
An aim of the present invention is to raise the degree of freedom of positioning of the valve chamber along the axial length of the valve housing and reduce the axial length and hence the mass of the movable core, making it possible to raise the degree of freedom of design, in such a normally closed electromagnetic valve.
An aim of the present invention is also to provide a normally closed electromagnetic valve which allows easy incorporation of the valve housing in the substrate as well as easy detachment of the valve housing from the substrate to give an enhanced mountability and recyclability.
The aforementioned aim of the present invention is accomplished with a first aspect of the present invention, that is a normally closed electromagnetic valve having: a cylindrical valve housing having a thin wall; a valve seat member fitted in and fixed to one end of the valve housing; a fixed core fixed liquid-tightly to the other end of the valve housing; a movable core forming a valve chamber with the valve seat member and housed in the valve housing so as to be opposed to the fixed core; a valve body fixed to the movable core seatably on a valve seat formed on the valve seat member facing the valve chamber; a return spring provided between the fixed core and the movable core and giving a spring force that causes the valve body to be seated on the valve seat; and, a coil for generating an electromagnetic force that causes the movable core to be attracted to the fixed core during excitation, wherein a large diameter portion is provided in the axially middle portion of the valve housing. In the first aspect, it is preferable that the cylindrical valve seat member forms an annular chamber with the inner surface of the large diameter portion, the annular chamber communicates to the valve chamber, and is fixed to and fitted in one end of the valve housing and communicating holes through which the annular chamber is communicated to the exterior of the valve housing are provided in the large diameter portion. In the first aspect, it is preferable that one side of the valve housing is housed in a mounting hole opened on one end of a substrate so as to be restricted in axial movement thereof toward the interior of the mounting hole.
In this arrangement, the degree of freedom of predetermination of position of communicating holes can be enhanced. In other words, in the case where the valve housing is in the form of simple cylinder which is uniform in diameter all over the axial length, it is necessary that the valve chamber and the communicating holes are at substantially the same position along the axial length of the valve housing. When the valve housing is provided with a large diameter portion, an annular chamber communicating to the valve chamber can be formed between the valve housing and the valve seat member. In this arrangement, the degree of freedom of positioning of the valve chamber along the axial length of the valve housing can be raised, making it possible to reduce the axial length and hence the mass of the movable core and hence raise the degree of freedom of design.
According to a second aspect of the present invention, the normally closed electromagnetic valve as set forth in the first aspect, further having retaining units for keeping one end of the valve housings housed in the mounting hole in contact engagement with the stepped portions; and a solenoid portion removably fitted on the protrude portion of the valve housings from the substrate so as to include the coil, wherein the retaining units are detachably provided in the substrate and the solenoid portion is supported on a cover which is detachably mounted on the substrate and covers the solenoid.
In accordance with the inventive constitution defined in the second aspect, the retaining unit is mounted on the substrate with the valve housing housed in the mounting hole on one end thereof, making it possible to easily incorporate the valve housing in the substrate. By removing the retaining unit from the substrate, the valve housing can be detached from the mounting hole on the one end thereof. Further, since the protrusion of the valve housing from the substrate is removably housed in the solenoid portion including a coil, the solenoid portion including a coil can be easily separated from the valve housing by removing the cover supporting the solenoid portion from the substrate. Thus, the valve housing can be incorporated in or removed from the substrate on one end thereof. By mounting the cover on the substrate with one end of the valve housing incorporated in the substrate, the protrusion of the valve housing from the substrate can be housed in the solenoid portion to form the entire normally closed electromagnetic valve. Accordingly, the valve housing can be easily incorporated in the substrate and removed from the substrate, making it possible to enhance mountability as well as recyclability.
According to a third aspect of the present invention, the normally closed electromagnetic valve as set forth in the second aspect, wherein the retaining unit includes a retainer ring housed in the mounting hole and contacting and engaging with the stepped portion, and a retaining ring detachably mounted on the inner surface of the mounting hole and contacting and engaging with the retainer ring on the axially external side of the mounting hole. In this arrangement, by receiving the valve housing in the mounting hole of the substrate on one end thereof with the retainer ring kept in contact engagement with the stepped portion of the valve housing and mounting the retaining ring on the external end of the mounting hole in contact engagement with the retainer ring, the valve housing can be mounted on the substrate, making it possible to easily incorporate the valve housing in the substrate and hence improve mountability. Further, the retaining ring can be removed from the external end of the mounting hole, making it easy to remove the valve housing from the mounting hole.